1. Field of the Invention
The present invention relates to a method of configuring a direction-based Core Based Tree (CBT) for a CBT-based overlay multicast.
2. Description of the Related Art
Generally, when one intends to transmit the same information to several receivers, one-to-many communication for transmitting data only to receivers participating in a corresponding multicast group through a multicast is more efficient than a unicast, i.e., one-to-one communication, since the one-to-many communication can reduce receiving side latency, use of network resources, and transmission overhead of a transmitter.
However, in an Internet Protocol (IP) multicast performed over a network, the network must be configured using a multicast router for relaying data according to a multicast routing algorithm.
Accordingly, there is a drawback in that a new investment cost is required for replacing a conventional unicast router with the multicast router.
On the other hand, on an Internet Service Provider's (ISPs') side, due to a low investment profit caused by the absence of a multicast service profit model and also on a technical side, due to a negotiation and a policy for passing through a multicast traffic between Session Initiation Protocols (SIP), a fairness with a conventional unicast traffic, and a still unclear inter-domain multicast technology, etc., the introduction of multicast has been delayed in an ISP backbone network.
Meanwhile, private and local multicast requests have rapidly increased, foe example, company broadcasting and campus broadcasting, etc. using the Internet. Accordingly, there is a need for multicast transmission based on a current unicast network.
An overlay multicast for relaying data in a terminal node is one method for a unicast-network-based multicast transmission. Due to a recent rapid improvement in data processing speed and a rapid improvement in data transmission speed in accordance with the increase of memory capacity and the spread of VDSL, etc., the terminal node performs the relay of data to other terminal nodes so that an efficient overlay multicast can be expected.
FIG. 1A illustrates a network configuration for performing an Internet Protocol (IP) multicast using a multicast router, and FIG. 1B illustrates a network configuration performing an overlay multicast using a unicast router.
A basic concept of the overlay multicast is that, instead of performing the multi cast over the network consisting of multicast routers (MR1-MR4) as shown in FIG. 1A, it can perform a unicast-based multicast by relaying (transmitting after copying) a packet in the terminal node (host) such as a node B in the network consisting of unicast routers (R1-R4) as shown in FIG. 1B. That is, the terminal node can perform a role of the multicast router.
In comparison with the multicast performed over the network of FIG. 1A, the overlay multicast performed over the network of FIG. 1B increases delay time or number of packets, but it does not need the multicast router, thereby providing a relatively efficient multicast communication based on the conventional unicast network.
Research is now progressing on an overlay multicast protocol, a distance vector multicast routing protocol (DVMRP), a narada to which the multicast routing protocol is applied, installing a scattercast proxy on the network to use the unicast communication between proxies, and CBT.
A core of such an overlay multicast is that an overlay tree for an efficient packet transmission is configured and maintained using terminal nodes included in the same multicast group.
On the other hand, the CBT to which a shared tree is applied is more efficient than the DVMRP to which a multicast routing protocol is applied, in an extension, an overhead of a control message, and performance.
That is, the CBT has a disadvantage in that traffic is converged on the core node, but has advantages in that relatively fewer control messages are generated for a variation of a multicast member and in that the quantity of information managed in each of the terminal nodes becomes smaller, to make an extension better and to make its realization easier. Further, since, in proportion to an improvement in the processing speed of the terminal node and an improvement in data transmission capacity, the number of relay-able child nodes is increased to improve performance of an overall multicast, thereby making the CBT-based overlay tree configuration more efficient.
The CBT-based overlay multicast basically selects a node to which a node-to-node distance comes close as a parent or a child node to configure the CBT. In the CBT metrically measuring the distance, a procedure of relaying packets to all nodes on the CBT is performed so that it repetitively passes the packets to a specific link or router, thereby causing traffic to be converged on the corresponding link or router to bring about congestion.
Generally, since the multicast is operated according to a user datagram protocol (UDP) not having a congestion control mechanism, unlike a transmission control protocol (TCP), even when congestion is generated on the network, the packet can continuously be transmitted to the network without reducing the quantity of traffic. As a result, there are drawbacks in that network performance as well as multicast performance can deteriorate due to the packet loss and in that an unfair problem with other TCP connections on the network can be caused.
The following patents each discloses features in common with the present invention but do not teach or suggest the inventive features disclosed in the present application: U.S. Patent Publication No. 2003/0088696 to McCanne, entitled PERFORMING MULTICAST COMMUNICATION IN COMPUTER NETWORKS BY USING OVERLAY ROUTING, published on May 8, 2003; U.S. Patent Publication No. 2003/0195964 to Mane, entitled MANAGING MULTICAST SESSIONS, published on Oct. 16, 2003; U.S. Patent Publication No. 2003/0185209 to Lee, entitled SCALABLE IP MULTICAST WITH EFFICIENT FORWARDING CACHE, published on Oct. 2, 2003; U.S. Patent Publication No. 2003/0058857 to Maher et al., entitled MULTICAST IP ZONES FOR FAST SPANNING TREE CONVERGENCE IN WIDE-AREA PACKET NETWORK SYSTEMS, published on Mar. 27, 2003; U.S. Patent Publication No. 2003/0005149 to Haas et al,. Entitled INDEPENDENT-TREE AD HOC MULTICAST ROUTING, published on Jan. 2, 2003; U.S. Patent Publication No. 2002/0091846 to Garcia-Luna-Aceves et al., entitled TREE-BASED ORDERED MULTICASTING METHOD, published on Jul. 11, 2002; U.S. Patent Publication No. 2002/0143951 to Khan et al., entitled METHOD AND SYSTEM FOR MULTICAST TO UNICAST BRIDGING, published on Oct. 3, 2002; U.S. Pat. No. 6,625,773 to Boivie et al., entitled SYSTEM FOR MULTICAST COMMUNICATIONS IN PACKET SWITCHED NETWORKS, issued on Sep. 23, 2003; U.S. Pat. No. 6,611,528 to Farinacci et al., entitled HIERARCHICAL ROUTING KNOWLEDGE FOR MULTICAST PACKET ROUTING, issued on Aug. 26, 2003; U.S. Pat. No. 6,321,270 to Crawley, entitled METHOD AND APPARATUS FOR MULTICAST ROUTING IN A NETWORK, issued on Nov. 20,2001; U.S. Pat. No. 6,078,590 to Farinacci et al., entitled HIERARCHICAL ROUTING KNOWLEDGE FOR MULTICAST PACKET ROUTING, issued on Jun. 20, 2000; and U.S. Pat. No. 6,611,872 to McCanne, entitled PERFORMING, MULTICAST COMMUNICATION IN COMPUTER NETWORKS BY USING OVERLAY ROUTING, issued on Aug. 26, 2003.